My thoughts on this issue are a wee bit complex.
Does more power lower down (forget boost, boost is just shoving more air in, that in itself isn't going to do anything strain wise) increase strain on rods/crank vs the same power higher up?
- At particularly low revs and high load the burn may complete before the crank angle has changed all that much, while at first thought one might think that it would put undue force on bearings and things, I don't believe so, since that force is still going to be applied higher up. It's the same force however the engine speed is high enough that the burn is not unduly fast.
- There's a psychological element to it since 'lugging' feels bad (and causes carbon buildup), but I am doubtful that lugging actually puts any significant extra strain on the bottom end unless the timing is unduly advanced where detonation takes over as the cause of trouble.
- In terms of strain vs RPM. The crank is definitely under greater strain at higher RPM as it is moving faster and therefore, while the _amount_ of instantaneous strain (or strain per revolution even) doesn't change, it is occurring more often/shorter time and therefore total strain for the same time period is greater.
Regardless of the above thoughts, is it anything to worry about?
- I honestly don't think so given that many modern turbo european cars (VW Golf, Audi A1 are the two I'm looking at in this instance) run compression ratios greater than 9.5:1 (2010 Golf GTI, 9.6:1 as per http://www.netcarshow.com/volkswagen/2010-golf_gti/ ) and spool to full boost by about 1800rpm. Subaru also have done this in the past, BC5 and BF5s equipped with the VF10 spooled to full boost by around 1600-1800rpm and the BE5D TT spools to 1bar+ by 1400rpm.
Looking at the above points I personally disagree with Sultan/Mike and concur with MercuryFree/Rob